1. Field
This invention relates to integrated protective impregnation deposition into nuclear cladding.
2. Description of Related Art
The exposure of zirconium cladding to the high-temperature and high pressure water environment in a nuclear reactor can result in the corrosion (oxidation) of the surface and consequent hydriding (due to the hydrogen release into the metal from the oxidation reaction with water) of the bulk cladding, ultimately leading to metal embrittlement. This weakening of the metal can adversely affect the performance, life-time, and safety margin of the nuclear fuel core. Recognizing this, many attempts to coat the zirconium outer surface with one or more layers of various materials have been tried, for example, Knight et al., Bryan et al., Van Swam and Lahoda et al. (U.S. Pat. Nos. 6,231,969; 5,171,520; 6,005,906; and 7,815,964, respectively). The simple inclusion of an oxidation resistant coating on the zirconium surface can, in theory, protect the zirconium substrate from the reactor environment; however, strong adherence of the coating to the zirconium substrate is problematic due to a fine oxidation layer that always exists on top of the zirconium surface as shown in prior art FIG. 1. These prior art processes often result in the coating peeling or spalling off the oxide surface when the coated cladding is exposed to prior art reactor operating conditions.
Knight et al. disclose a discrete coating such as Ti3SiC2 with less than 30% porosity with a thickness between 0.002 inch and 0.005 inch. Bryan et al. disclose initial heating of the cladding from 300° C. to 400° C., and flame spraying a mixture of zircon, about 30 micrometers, diameter and glass binder, less than 10 micrometers, to provide an intermixed discrete coating on the cladding.
Lahoda et al. disclose abrading the surface of the zirconium cladding to remove oxides and surface deposits, and spraying boron, gadolinium, hafnium, erbium, HfB2, ZrB2, Gd2O3, or Er2O3 or their mixtures—all burnable poisons having particle sizes from 1 micrometer to 250 micrometers, at a velocity of from 1,500 ft./sec. to 2,500 ft./sec. (457 meters/sec. to 762 meters/sec.). This initiates a surface phase change at the exterior surface of the cladding, so some molecular melting occurs (inter-atom bonding or forming craters) and the impacting particles provide a still discrete impacted surface coating. Van Swan provides discrete “coatings”/layers of different oxygen content zirconium claddings, as many as three.
Knight et al. further disclose coating processes ranging from dipping/painting, chemical adsorption and thermal spraying. Bryan et al. (U.S. Pat. No. 5,301,211) disclose a linear magnatron sputtering apparatus to uniformly coat zirconium alloy nuclear cladding in an atmosphere of argon gas. A variety of coating materials are mentioned, including TiN, TiAlN, TiC and TiCN. Coker et al. (U.S. Pat. No. 4,049,841) generally teach plasma and flame spraying techniques.
Cabrero et al. (U.S. Patent Application Publication No. US2011/0170653A1) disclose cladding totally or partially made of a composite of a SiC ceramic fiber matrix, in the form generally of random orientation, weaves, knits or felts. This can include several superimposed layers. This matrix includes a carbide, for example, TiC and Ti3SiC2.
What is needed is a new type of protective means; a main object of this invention is to provide this and solve the problems described above.